1. Field of the Invention
The present invention relates to an antenna system, and, more particularly, to an air leak detection device for an antenna system.
2. Description of the Related Art
Typical microwave antenna systems include a transmission line, a feed horn and a reflector dish. There are many types of configurations of these components depending upon the antenna type and frequency range. The transmission line conducts radio frequency signals to and from the feed horn. The feed horn operation is critical to the proper operation of the entire antenna system. The fundamental purpose of the feed horn is to match the impedance of the transmission, which may typically be 50 ohms to that of free space, which is approximately 377 ohms. At typical microwave frequencies, such as in the C band and above, the transmission line is also commonly called a waveguide that is normally hollow. The feed horn itself, often called the feed, includes a conical structure that is hollow and is connected to the waveguide.
Often the feed horn is mounted so that it is offset from the center of the reflector. The reflector may be a section of a parabola and the offset feed scheme prevents the feed and the feed support from shading the reflector and thus reducing its effective aperture for other performance problems.
The offset feed scheme often requires the feed horn to be positioned such that rain, water or snow may enter therein. If water enters the feed horn it causes corrosion and signal loss. This problem is further exasperated by the flow of water into the radio frequency components used in the receiver/transmitter. Typically the opening in the feed horn is covered with a membrane, such as a plastic membrane to shield the system and to prevent the entry of water thereby. The plastic membrane must pass radio frequency energy with minimum attenuation. This imposes a limit on the material that can be used for constructing the membrane. Typical membranes are sensitive to sunlight and more particularly to the ultraviolet light that causes the membrane to become brittle and crack.
The radio frequency components are substantially hermetically sealed and while leakage often occurs through the membrane it is also understood that other portions of the feed horn, waveguide or radio frequency components can also allow ambient air to leak into the interior thereof. Leakage can be the result of leaking gaskets, fatigue cracks in the transmission line or other components as well. Ambient air contains gaseous water and when the ambient temperature falls to or below the dew point, condensation will occur within the system. Water that condenses therein is typically too viscous to escape and it remains trapped inside of the radio frequency components causing corrosion damage and it also modifies the impedance of the transmission line and feed horn. The most popular method of keeping the interior of the radio frequency components from the radio/transmitter all the way to the feed horn is to pressurize the system with low-pressure dry air. The pressurized dry air may slowly leak through the various openings in the antenna system but this prevents moist ambient air from leaking thereinto. Typical pressures range from 0.25 to 6 lbs per square inch above the ambient pressure. The supply of the dry air will typically have a dew point that is below −50° C.
The pressurized air may be supplied by way of a small compressor and an air-drying system. A typical installation may have four to eight or more antenna systems that utilize the pressurized dried air from the single supply source.
A leak in one of the antennas can compromise the ability of the rest of the antennas to be adequately protected since the compromise depletes the supply of dried pressurized air. A substantial leak in one antenna then can lead to the eventual failure or degradation of the rest of the antennas since they are all then starved for the necessary pressurized dry air.
What is needed in the art is a device and system that will detect and isolate a leak of air in an antenna system.